I have this posted over on ih8mud, but thought I would throw it out over here. I have this popping noise comming from up front. It only happens when:

The axle articulates (not much is needed just a bump will do).
Not speed related, in fact, I dont hear it at cruising speed.
happens a bit more when turning.

I have put it up on jack stands level and articulated and couldnt get it to happen with the steering being moved. Nothing in the steering is binding. Yesterday, I pulled both birfs and gave them a thorough look, nothing is out of the ordinary there either, they both look and operate great.

Some guys have suggested springs are suspect, and I should try oiling them, any other thoughts?

I am hoping for a nice ride up Conney Flats next weekend and I want to find out what this noise is and correct it.

I don't think it is the birfs because I just pulled them yesterday and there was nothing visually to make me think they were not in good shape. No binding, not wear marks, no pitting, no cracks, everything looked and operated great.

Did you pull the birfields apart? If not then you did not fully inspect them. In reading your post, it sounds like it pops in 2 wheel drive with the hubs disengaged? If this is correct then the Birf are not the problem. Have some one else turn the steering wheel when you are in front, this may help you find the problem. Look at tie rod ends, look bolts, shifting shackles, any thing under the front end. later robbie

I had the same symptom, but I knew exactly what it was based on when and how it happened. Tightened up the front spring pack u-bolts and no more clunk/bumping while articulating/turning. These were new u-bolts when I lifted a year and a half ago, I had retorqued them after about 100 or so miles, but they still needed to be retorqued again after a couple thousand.

The sound was caused by the leaves shifting around within the packs. This may not be the cause of your sound, but it was for mine.